Method for preserving food products

ABSTRACT

A method for preserving a food product, such as meat, is provided. The method comprises the steps of inoculating meat with an effective amount of euhygienic non-pathogenic, non-spoilage bacteria in order to competitively inhibit the growth of undesired pathogenic and spoilage bacteria. Preferably, either L. delbrueckii or Hafnia alvei bacteria are used to inoculate a meat product. Bacteria present on a meat product is first reduced to a number below about 5000 bacteria per gram of meat, e.g. by dehairing an animal and then spraying the meat with an organic acid prior to inoculation with euhygienic bacteria. The meat product is then vacuum packaged and stored in a refrigerated environment of about -1° C. to about 7° C. Meat products preserved in accordance with the method of the invention can enjoy a refrigerated shelf life of up to about 150 days without surface discoloration or the generation of undesirable gaseous by-products.

FIELD OF THE INVENTION

This invention relates to a method for preserving food products, andparticularly meat and meat by-products and food products producedthereby. More particularly this invention relates to a method forpreparing a meat product having a shelf life of up to 150 days bydehairing an animal, removal of the hide of the animal, contacting theanimal carcass with weak organic acids, and inoculating meat witheuhygienic bacteria to competitively inhibit and/or exclude the growthof undesired pathogenic and spoilage bacteria.

BACKGROUND OF THE INVENTION

In the meat industry, and particularly in those areas devoted to theprocessing of beef and pork, meat packers slaughter animals in a processin which the animals are stunned, bled, skinned, eviscerated, andfabricated into meat sections which are then marketed in grocery storesand in the restaurant trade. Animals enter a meat slaughter plant withvarious foreign materials present on their hair, including blood, dirt,manure, mud, and vegetative material. An animal's hair is alsocontaminated with a multitude of microorganisms, some of which arepathogenic to humans. Most bacteria present in a meat slaughtering andprocessing facility are carried into the facility on the hides ofanimals to be slaughtered. During the slaughtering process thesemicroorganisms contact meat and other meat by-products, therebycontaminating such products, creating handling problems and reducing theshelf life and safety of the meat products.

The control of contamination by microorganisms is a recognized problemin the meat packing industry. The preparation of food products, andparticularly fresh meat and meat products for the retail market, islargely concerned with the control of microbial contact with food inorder to increase the shelf life of food products. Food products havingan extended shelf life afford more time in which handlers, shippers, andwholesalers can transport and sell such food before spoilage occurs.Efforts to increase the shelf life of food products, such as meat, havetraditionally been focused on reducing the number of bacteria present onthe surface of the food product.

Freezing food, and particularly meat, has proven to be an effective wayin which to retard the growth of bacteria that may be present on thesurface of the food. The freezing of meat, however, especially forextended periods of time, has many undesirable effects. By freezing ameat product, water within the meat crystallizes, causing the denaturingof proteins and other damage to the meat on a cellular level. Moreover,the texture, consistency and taste of thawed frozen meat is lessdesirable than that of fresh meat. Because of the relative short shelflife of fresh meat, foreign markets can only be reached by freezingdomestic meat products. Many foreign meat consumers, such as those inthe Pacific rim countries and Europe, prefer fresh meat to frozen meat.Such fresh meat preference effectively preclude foreign sales ofdomestic meat. Without freezing the meat product, however, the bacteriathat has contacted the meat during processing are able to proliferate,creating spoilage and pathogenic concerns.

The opportunity for bacterial contact with the fresh meat begins when ananimal is initially presented for processing and extends up until thetime the meat product is consumed. The initial bacterial contact withfresh meat is encountered with a meat processing facility due to thecontaminated state of the animal when it enters the facility. Furtheropportunities for bacterial contact arise from the significant amount ofhuman handling and equipment exposure during the slaughter, processing,and transportation of meat products. Moreover, when consumers remove thewrapping of a meat product for cooking, additional opportunities presentthemselves for bacterial infection.

The time between the initial opportunity for bacterial contact with meatproducts and the ultimate consumption of such products by consumers,allows for the proliferation of various forms of bacteria, including thegrowth of undesired spoilage and pathogenic bacteria. The growth ofundesired bacteria on meat presents aesthetic concerns affecting themarketability of meat products. For example, growth of spoilage bacteriacreates undesired odors due to bacterial production of certain esters,hydrogen sulfide, nitrogenous compounds, ruturic acid, propionic acid,formic acid, as well as other undesirable gases and acids. The growth ofother such bacteria also acts to discolor the surface of the meat.Moreover, when meat packaged in permeable plastic packages spoils, thepackaging often inflates due to the generation of gas produced byspoilage bacteria.

Contamination of meat with pathogenic bacteria is also a great concernsince such bacteria, or toxins produced by such bacteria, can causeillness or disease in humans and animals who consume such meat. Theshelf life of a meat product is directly related to the number ofspoilage and pathogenic bacteria present on the surface of the meatproduct. A meat product having a high level of spoilage and pathogenicbacteria on its surface exhibits a relatively short shelf life, whereasmeat having a low count of spoilage and pathogenic bacteria exhibit anextended shelf life.

There has been a long felt need in the meat packaging industry forcontrolling undesired bacterial proliferation in order to avoid spoilageand thereby increase the shelf life of meat products. Governmentstandards also mandate that meat processing facilities attain certaintolerances which have been set regarding the number of potentiallyhazardous bacteria that meat may contain. Methods by which undesiredbacterial growth on meat can be controlled are therefore desired.

In a meat processing facility, animals are slaughtered and fabricated ina process which progressively disassembles the animal to produce meatcuts for sale to customers. When an animal to be slaughtered enters aprocessing facility, it typically has a great variety of bacteriapresent on its hide. Bacteria present on an animal primarily originatefrom the foreign material present on an animal's hide, including blood,dirt, manure, mud and vegetative material. The necessary handling ofmeat products during the fabrication process provides additionalopportunities for meat to come into contact with bacteria. Inconventional meat processing facilities, it has not been economicallyfeasible to remove all sources of material contact with the meat or tomaintain perfect environmental conditions to retard bacterial growth.

The prior art utilizes several methods to prolong the retailacceptability of meat products. For example, vacuum packing of meat ingas permeable packages is commonplace. Irradiation with ultravioletlight has been used to reduce the number of microorganisms on meatsurfaces. Salting of meat has long been practiced to preserve meatproducts. Refrigeration is also widely used to deter the rapid growth ofspoilage and pathogenic bacteria on meat products. Spoilage bacteria,such as pseudomonas, are known to grow most rapidly at about roomtemperature. Although such bacteria are present on meat at lowertemperatures, their growth is significantly slowed by coolerenvironments. Mere refrigeration alone, however, is not totallyeffective in preventing or adequately retarding the growth of spoilageor pathogenic bacteria for any appreciable amount of time.

The shelf life of meat has also been extended somewhat by the use ofchemical agents. Chemical treatment of meat to destroy surface bacteriahas traditionally been accomplished by treating meat with weak acidsand/or chlorine solutions. These conventional techniques, however, oftencreate undesirable color, flavor and order modifications of meat, andare often ineffective to maintain meat in a saleable condition for anyappreciable period of time.

Although the control of spoilage and pathogenic bacterial growth is arecognized problem in the meat packing industry, the reduction of meatshelf life attendant to such growth continues to be a significantproblem. Many techniques have been employed in the past in an effort todestroy surface bacterial flora on meat. For example, U.S. Pat. No.4,852,216 to Clayton discloses a disinfection system using an aceticacid spray in order to reduce bacterial levels and thereby increaseshelf life of meat products. Similarly, U.S. Pat. No. 3,924,044 to Buschdiscloses a method for applying a hot, dilute acid solution to meatsurfaces to destroy psychotropic spoilage bacteria on meat surfaces.U.S. Pat. No. 3,991,218 teaches the encapsulation of meat products in afilm of alginate material to retard the growth of anaerobic bacteria onthe surface of the meat. Other inventors have utilized anti-microbialagents for preserving products normally subject to microbial spoilage.For example, U.S. Pat. No. 3,915,889 to Jurd discloses a certainanti-microbial agent that can be applied for preservation for a widevariety of substances including meat.

Other inventors have recognized the advantages of dehairing animals tofacilitate the slaughtering process. U.S. Pat. No. 4,674,152 to Georgesdiscloses an apparatus and method for slaughtering animals by bleedingan animal, electrostatically charging the animal's hair, applying acombustible fluid to the hair and subsequently igniting the combustiblefluid to burn the hair from the animal's body. U.S. Pat. No. 4,309,795to Simonsen discloses a method and apparatus for de-hairing hogs whereinthe hog is bled, its skin is scalded with hot water, and then subjectedto abrasive treatment to remove the hogs hair.

In a direct teaching away from the present invention, other researchershave concluded that contacting meat products with lactic acid bacteria,and thereafter vacuum packaging such meat in impermeable plastic, isineffective in controlling the growth of pathogenic and spoilagebacteria on the meat. For example, the companion articles by Hanna etal., "Inoculation of Beef Steaks with Lactobacillus Before VacuumPackaging, I. Microbiological Considerations," Journal of FoodProtection, Vol. 43, pp. 837-841 (November 1980) and Smith, G. C. etal., "Inoculation of Beef Steaks with Lactobacillus Species BeforeVacuum Packaging. II. Effect on Meat Quality Characteristics," Journalof Food Protection, Vol. 43, pp. 842-849 (November 1980) disclose thatdisadvantages outweigh advantages for inoculation of beef withLactobacillus cultures prior to vacuum packaging of meat. In addition,Egan et al., "Significance of Lactobacilli and Film Permeability in theSpoilage of Vacuum-Packaged beef," Journal of Food Science, Vol. 47, pp.119-126 (1982) disclose that even in the absence of a significantpopulation of contaminating microorganisms, sterile vacuum packaged beefhas a limited shelf life and the addition of Lactobacillus bacteria tovacuum packaged meat increases the rate of spoilage. Therefore, no priorart techniques have taught the effective elimination of growth ofundesired bacteria to achieve a significant extension of shelf life infresh meat products.

In the meat packing industry, many types of bacteria are known to causefood poisoning including: E. coli, Salmonella, F. coliforms, Listeria,Staphylococcus, F. streptococcus, Bacillus anthraces, Balantidium coli,Campylobacter coli, Campylobacter jejune, Francisella tularensis,Sarcocystis, Taenia saginata, Taenia solium, Toxoplasma gondil,Trichinella spiralis, Yersinia enterocolinea, Yersiniapseudotuberculosis, Brucella, Chlamydia petechia, Leptospira andClostridium. These pathogenic bacteria each group and proliferate underdifferent conditions, any or all of which may be present in a meatprocessing facility. For example, Listeria is generally found in cool,damp environments such as coolers and meat processing areas.Staphylococcus is often found on cattle hair, in fecal material, ininfected cuts and internal abscesses, and is sometimes associated withpoor hygienic practices of food handlers.

Spoilage bacteria, including psychotropic bacteria such asPseudomonades, Lactobacillus and Coliform, affect the shelf life of meatproducts by causing discoloration of meat and undesired odors. Thesebacteria are typically found in soil, ingesta, and fecal material thatare commonplace on an animal's hide.

The bacteria present on an animal's hide can be roughly divided intothree distinct categories: pathogenic bacteria, lactic bacteria, andspoilage bacteria. In the environment of a meat processing facility,spoilage bacteria typically proliferate at a greater rate than dopathogenic bacteria or lactic bacteria. It has been recognized thatvarious sanitizing techniques, including acetic acid sprays, applicationof anti-microbial agents, and irradiation, can be used to reduce thetotal number of bacteria present on an animal carcass. However, whilethe total number of bacteria can be reduced, it is difficult tospecifically kill pathogenic and spoilage bacteria without eliminatingall the bacteria present on an animal carcass.

Additional difficulties are experienced in the control of certain typesof bacteria, namely Salmonella and Listeria, which initially infect meatby implanting themselves on meat surfaces. After contact, such bacteriaimmediately initiate the secretion of a waxy material to protectthemselves from the outside environment. Unless these bacteria arecontacted with chemical agents, such as acetic acid, before significantimplantation and secretion of waxy substances, such bacteria areextremely difficult to remove from the meat.

Conventional wisdom in the meat processing industry teaches themaintenance of low bacterial counts as measured by the total number ofbacteria on a meat product. For example, if bacterial counts exceedabout ten million bacteria per gram of meat, the meat is disposed of asa matter of course. However, a total bacterial count includes not onlythe number of pathogenic and spoilage bacteria, but also non-pathogenic,non-spoilage bacteria.

In view of the above, a need exists for a method for preserving foodproducts, particularly fresh meat and meat by-products, by selectivelyreducing the number of spoilage and pathogenic bacteria present on suchfood products.

SUMMARY OF THE INVENTION

The present invention includes a method for preserving food products,such as meat, by inoculating such food products with an effective amountof euhygienic bacteria. Euhygienic bacteria are non-pathogenic and/ornon-spoilage bacteria able to competitively inhibit and/or exclude thegrowth of pathogenic and spoilage bacteria. The euhygienic bacteria usedin the present invention create essentially no malodors or discolorationof food products, such as meat, and thus act to extend the shelf life offoods products. The present invention specifically is applicable to thepreservation of meat from poultry, beef, pork, lamb, fish and seafood,as well as to dairy products, vegetables, fruits and grains.

In one embodiment of the invention, euhygienic bacteria are preferablyfacultative, sacrophilic, gram positive bacteria, and more preferablybacteria of the genus Lactobacillus. Euhygienic bacteria are preferablyobligately homofermative lactobacilli but can also be facultativelyheterofermentive lactobacilli.

In another embodiment of the invention, euhygienic bacteria includeLactobacillus delbrueckii, L. leichmannii, L. jensenii, L. lactis, L.bulbaricus, L. helveticus or L. acidophilus. In a preferred embodimentof the invention the euhygienic bacteria are predominately of thespecies L. delbrueckii or Hafnia alvei, or a combination of L.delbrueckii and Hafnia alvei.

In accordance with one embodiment of the present invention, a foodproduct is inoculated with euhygienic bacteria able to proliferate attemperatures from about -1 C. to about 35° C. Another embodimentinvolves reducing the number of bacteria present on a food product,preferably below about 5000 bacteria per gram of food product, prior toinoculation with an effective amount of euhygienic bacteria. Inoculationof a food product is performed prior to packaging of the food product,preferably with impermeable plastic wrapping. In one embodiment of thepresent invention freeze dried euhygienic bacteria are placed inside afood package prior to sealing of the package. Reduction of the number ofbacteria on a food product may be accomplished in various ways includingirradiating the food, exposing the food to elevated temperatures,contacting the food with antibiotics, or contacting the food with anorganic acid such as lactic or acetic acid.

In yet another embodiment of the invention, the surface of a foodproduct is inoculated with Hafnia alvei bacteria. Hafnia alvei bacteriaare believed to initially colonize the meat surface and create anenvironment conducive to the growth of L. delbrueckii bacteria. Thesubsequent or coincidental inoculation of the meat with L. delbrueckiicompetitively inhibits and/or excludes the growth of undesiredpathogenic and spoilage bacteria.

The present invention also includes the adjustment of the pH on thesurface of meat to create an environment conducive to the growth ofeuhygienic bacteria. In one embodiment of the invention, meat iscontacted with lactic or acetic acid to establish a meat surface pH ofabout 4 to about 7, and more preferably to between about 4 and 5,permitting the selective growth of euhygienic bacteria, such as L.delbrueckii or Hafnia alvei, over the growth of pathogenic and spoilagebacteria.

In another embodiment, an animal carcass, or meat therefrom, isinoculated with euhygienic bacteria after application to the carcass ofan organic acid, such as acetic or lactic acid, and prior to the vacuumpackaging of the meat in oxygen impermeable wrapping.

A further embodiment of the method includes maintaining an animalcarcass or meat therefrom at a temperature of about -1° C. to about 7°C. after inoculation with an euhygienic bacteria. In alternativeembodiments, the total number of bacteria present on an animal carcassis reduced and the animal carcass is inoculated with an effective amountof euhygienic bacteria able to produce antibiotics toxic to pathogenicand spoilage bacteria.

The present invention also includes food products prepared in accordancewith the above mentioned method. Specifically, in one embodiment of theinvention a meat product is produced having a shelf life of over about40 days and up to about 150 days with its surface primarily populatedwith euhygienic bacteria.

Other embodiments of the invention are directed to the reduction ofmalodors, and/or discolorations of food products, the inhibition ofundesired bacterial growth on food products, and the tenderizing of meatproducts by inoculating food or meat products with an effective amountof euhygienic bacteria. Another embodiment of the invention includes theeffective reduction of the growth of spoilage and pathogenic bacteriawithin a food processing facility by inoculating the food processingfacility and/or equipment therein, with an effective amount ofeuhygienic bacteria.

DETAILED DESCRIPTION OF THE INVENTION

In the preparation of a food product, and particularly a meat product,for animal or human consumption, one of the paramount concerns is toreduce the number of bacteria present on the surface of the foodproduct. The reason bacterial control on a food product is so importantis that certain types of bacteria, namely pathogenic and spoilagebacteria, shorten the shelf life of food products by multiplying on foodsurfaces, thereby generating undesired by-products that cause malodors,discoloration or poisoning of the food.

The term "food product" as used herein refers to any food that issusceptible to spoilage as a result of bacterial growth andproliferation on the surface of the food. Such food products include,but are not limited to meat, vegetables, fruits and grains.

As used herein, the term "meat" refers to any fresh meat product or meatby-product from an animal of the kingdom Animalia which is consumed byhumans or animals, including without limitation meat from bovine, ovine,porcine, poultry, fish and crustaceous seafood. Thus, while one of theprimary uses for the present invention relates to meat processed in theslaughtering of mammals in a meat processing facility, it is to beexpressly understood that the invention has application in theprocessing of other edible meat products including fish, poultry andseafood. Moreover, it is contemplated that the method also will have usein connection with the preservation of non-animal food products, such asfruits, vegetables and grains, subject to spoilage by bacterialmicroorganisms.

As used herein the term "shelf life" means the period of time that afood product remains saleable to retail customers. In traditional meatprocessing, the shelf life of fresh meat and meat by-products is about30 to 40 days after an animal has been slaughtered. Refrigeration ofmeat during this period of time largely arrests and/or retards thegrowth of pathogenic bacteria, and to a lesser extent, spoilagebacteria. After about 30 to 40 days, however, refrigeration is no longerable to effectively control the proliferation of spoilage bacteria belowacceptable levels. Spoilage bacteria present on meat products after thistime period are able to assimilate proteins and sugars on meat surfacesand begin to generate undesired by-products. Spoilage bacteria may alsoact to discolor meat, making such meat unappealing and undesirable forhuman consumption.

The term "spoilage bacteria" as used herein refers to any type ofbacteria that acts to spoil food. Spoilage bacteria may grow andproliferate to such a degree that a food product is made unsuitable orundesirable for human or animal consumption. Bacteria are able toproliferate on food surfaces, such as meat surfaces, by assimilatingsugars and proteins on such surfaces. By metabolizing these components,spoilage bacteria create by-products including carbon dioxide, methane,nitrogenous compounds, butyric acid, propionic acid, lactic acid, formicacid, sulfur compounds, and other undesired gases and acids. Theproduction of such by-products alters the color of meat surfaces, oftenturning meat from a red color to a brown, grey or green color. Gaseousby-products generated by spoilage bacteria also give spoiled meat anundesirable odor. The color and odor alterations of meat due to thegrowth of spoilage bacteria on a meat product's surface often makes suchmeat unsalable to consumers.

In addition to the control of spoilage bacteria, another significantconcern in the food processing industry is controlling the growth ofpathogenic bacteria. As used herein, the term "pathogenic bacteria"refers to any food poisoning organism that is capable of causing diseaseor illness in animals or humans. The term pathogenic bacteria will beunderstood to include bacteria that infect meat and thereby causedisease or illness, as well as bacteria that produce toxins that causedisease or illness. The proliferation of pathogenic bacteria on foodproducts can cause severe illness and may be deadly, as demonstrated bythe number of human fatalities caused by botulism. The term "undesiredbacteria" as used herein, refers to both spoilage and pathogenicbacteria. For purposes of illustration only and without being limitedthereby, the term "undesired bacteria" includes obligatelyheterofermentative Lactobacilli. Such bacteria ferment hexoses to lacticacid, acetic acid, ethanol and CO₂ and are also known to fermentpentoses to lactic acid and acetic acid.

Pathogenic and spoilage bacteria can be aerobic, anaerobic orfacultative, and thus, the elimination of oxygen alone from a foodpackage or from a food storage environment will not effectivelyeliminate all types of undesired bacteria. Moreover, control of thetemperature in the storage of food is not totally effective to precludethe growth of such bacteria because several types of pathogenic andspoilage bacteria are able to grow at various temperatures. Whileexposure to very high temperatures is known to be effective in killingmost bacteria, such exposure may damage at least a portion of a foodproduct by essentially cooking the food. High temperatures may also actto denature enzymes necessary for desired aging of meat products.Moreover, certain pathogenic bacteria produce toxins that are notdestroyed by exposure to elevated temperatures. Thus, raising thetemperature of food is not a practical way in which to effectivelyeliminate the negative effects of pathogenic bacterial contamination ofa food product.

Conventional practice in the meat processing industry teaches that theless bacteria present on a meat product, the safer such meat productwill be for human consumption. Attempts have thus been made toessentially sterilize the surface of meat to control bacterial growththereon. As used herein, the term "sterilize" refers to the significantreduction of the number of bacteria from the surface of a food product.In a more specific sense, the term means effectively de-populating afood product's surface of bacteria. In one embodiment of the invention,the number of undesired bacteria on a food product is reduced to belowabout 5000 bacteria per gram of food product. Conventional methods forsterilizing food products, such as meat, include contacting meat withweak organic acids, applying anti-biotic substances to meat, exposingmeat to high temperatures and irradiating meat with high frequencyradiation or x-rays. These and other methods can be used in conjunctionwith the present invention to substantially reduce the number ofbacteria present on meat products. Such other methods include de-hairingof an animal prior to dispatching of the animal to remove microorganismsassociated with the animal's hair. One preferred method of de-hairing ananimal, and thereby vastly reducing the number of bacteria on theanimal's hide, is to contact a depilatory substance to an immobilizedanimal and subsequently to remove its hair prior to the slaughtering ofthe animal.

While effective in reducing the number and kinds of bacteria on foodproducts such as meat, the above-mentioned methods are not able tocontinuously control the growth of spoilage and pathogenic bacteria. Forexample, by sterilizing an animal carcass, post-sterilization bacterialcontact of the animal carcass by indigenous bacteria, includingpathogenic and spoilage bacteria, is still possible. When a meat productis essentially rid of all forms of bacteria, pathogenic and spoilagebacteria present in the ambient environment have a new opportunity tocolonize the animal carcass. Thus, once an animal carcass has beensterilized, it has traditionally been of utmost importance to maintain asterile environment to preclude the opportunity for additional contactof the meat by undesired bacteria.

Maintenance of an essentially sterile environment within a meat packingfacility, however, is practically impossible using current technology.As such, a method is needed that can preclude the growth of pathogenicand spoilage bacteria subsequent to the effective sterilization of ananimal carcass. The present invention fulfills this need by inoculatingmeat of an animal with a desired euhygienic, non-pathogenic,non-spoilage bacteria, immediately after the animal has been de-haired,had its hide removed, and sterilized. In such a manner, euhygienicbacteria are able to colonize the animal carcass and therebycompetitively inhibit and/or exclude the growth of undesired pathogenicand spoilage bacteria.

As used herein, the term "euhygienic bacteria" generally refers to ahygienic control bacteria that does not generate a significant orunacceptable amount of undesired by-products during its growth andproliferation. The term "euhygienic bacteria" is therefore understood toinclude non-spoilage bacteria as well as non-pathogenic bacteria. Theterm also includes any bacteria that may be genetically altered todelete or otherwise ameliorate qualities that would effect thesalability and/or edibility of a food product, including withoutlimitation bacteria altered to reduce production of carbon dioxide,methane, nitrogenous compounds, sulfur compounds, propionic acid,butyric acid, formic acid, as well as other undesirable compounds.

Euhygienic bacteria are preferably obligately homofermentativelactobacilli that ferment hexoses almost exclusively to lactic acid bythe Embeden-Meyerhof pathway. A preferred embodiment of euhygienicbacteria do not ferment gluconate or penroses.

Another type of euhygienic bacteria is classified as a facultativelyheterofermentative lactobacilli. This class of euhygienic bacteriaferment hexoses almost exclusively to lactic acid by theEmbeden-Meyerhof pathway. In addition, some species of euhygienicbacterial ferment hexoses to lactic acid, acetic acid, ethanol andformic acid under glucose limitation, and are known to ferment pentoseto lactic acid and acetic acid via an inducible phosphoketolase. In oneembodiment of the present invention, euhygienic bacteria arefacultative, sacrophilic gram positive bacteria that do produce minimalundesirable by-products during growth and proliferation.

The term "inoculation" as used herein, refers to any method foreffectively contacting bacteria to a surface so that such bacteria canproliferate on such surface. The surface of food products such as meat,as well as surfaces of food processing equipment, may be inoculated inany manner which effectively contacts desired bacteria to such surfaces.Such inoculation methods may include, but are not limited to, spraying asurface, such as an animal carcass, with effective amounts of, orimmersing an animal carcass in, a solution containing desired euhygienicbacteria. Inoculation of meat can also be performed by placing aneffective quantity of freeze dried euhygienic bacteria into a plasticbag with a meat product. The bag can then be evacuated of air and themoisture from the meat can then re-hydrate the freeze-dried bacteria,thereby allowing bacterial colonization of the meat. The general goalcommon to all inoculation methods is to contact a surface with asufficient quantity of euhygienic bacteria to colonize that surface andthereby inhibit and/or exclude the growth of undesired bacteria thereon.Inoculation of ground food products, such as ground beef, may beaccomplished by contacting the food product with euhygienic bacteriabefore, after, or during the grinding of the food products.

Euhygienic bacterial solutions can be prepared in acceptable amounts andunder appropriate environmental conditions, such preparation dependentupon various factors, such as the specific type of euhygienic bacteriaused, the food product to be inoculated and the type of undesiredbacteria to be inhibited and/or excluded. For example, an effectivesolution for inoculating meat with the euhygienic bacteria L.delbrueckii may be prepared by growing a culture of the euhygienicbacteria in a flask at a suitable temperature, e.g. about 35° C. forapproximately 24 hours. The solution can then be diluted with suitablemedium and applied to the meat. Dilution of euhygienic bacterialsolutions prior to application is also dependent upon the factors listedabove, with the general goal being the effective inoculation of a foodproduct with euhygienic bacteria able to competitively inhibit thegrowth of undesired bacteria. In one embodiment, for example, aneuhygienic bacterial solution is diluted to approximately one part ofbacterial broth grown in the above-described manner for every ten partsof additional media.

Preferably, euhygienic bacteria are applied to a food product during thelogarithmic growth phase of such bacteria. Therefore, euhygienicbacterial solutions should be formulated so that there is an ample foodsource available to support continued euhygienic bacterial growth andproliferation. A preferred food source media or broth for euhygienicbacteria comprises a mixture of simple and complex carbohydratesincluding but not limited to glycerol, ribose, galactose, D-glucose,D-fructose, D-mannose, N-acetyl-glucosamine, amygdalin, esculin,salicin, cellobiose, maltose, trehalose, and beta gentiobiose. In apreferred embodiment, the euhygienic bacterial growth broth ismaintained at a temperature of between 5° C. and 35° C. The resultingeuhygienic bacterial broth preferably has a pH of between about pH 4.1and about pH 4.6.

As used herein, the term "competitive inhibition" means the inhibitionof growth of undesired bacteria by creating an environment whereeuhygienic bacteria can competitively assimilate sugars and proteinspresent on a meat surface and thus, proliferate to effectively excludethe growth of undesired bacteria. The term "inhibition" as used herein,means the killing of a microorganism, such as an undesired bacteria, orthe control of the growth of a microorganism. As used herein, the term"exclusion" means the crowding out of one microorganism by another. Theterms "inhibition" and "exclusion" are collectively used herein to meanthe mechanism by which the growth of undesired bacteria is controlled toallow for the growth and proliferation of euhygienic bacteria.

Under one theory of how competitive inhibition operates, one type ofbacteria is able to competitively inhibit the growth of other forms ofbacteria by effectively proliferating to such an extent that other formsof bacteria are unable to contact the food surface. Because the growthof bacteria requires access to the surface of food in order toassimilate sugars and proteins thereon, bacteria first able to multiplyand occupy the surface of a food product can effectively preclude thegrowth of other forms of bacteria. Thus, to be effective in the presentinvention, euhygienic bacteria must be able to grow and multiply fastenough to substantially colonize a food surface before undesiredbacteria are able to significantly proliferate on the same surface. Byusing the present method, euhygienic bacteria are allowed to multiply,crowd out, and thereby exclude the growth of undesired bacteria, therebypreventing the spoilage and pathogenic infection of food.

In accordance with one embodiment of the present invention, meat isinoculated with an effective amount of euhygienic bacteria able tocompetitively inhibit and/or exclude the growth of pathogenic andspoilage bacteria. In this embodiment, the euhygienic bacteria used afacultative, sacrophilic, mesophilic gram positive bacteria. Moreparticularly, the present invention includes the use of euhygienicbacteria that are non-spoilage, non-pathogenic and acidophilic, thrivingin an environment with a pH of about pH 4 to about pH 5. While variouseuhygienic bacteria can be selected for use, preferred euhygienicbacteria include homofermentive bacteria able to produce either lacticacid or acetic acid as by-products of their glycolytic processes. Sucheuhygienic bacteria are thus able to create an environment favorable totheir continued proliferation but unfavorable to the growth of undesiredbacteria, i.e. Spoilage and pathogenic bacteria.

Preferably, a desired euhygienic bacteria is selected from the genusLactobacillus, and even more preferably from one or more of thefollowing species: L. delbrueckii, L. leichmannii, L. jensenii, L.lactis, L. bulgaricus, L. helveticus, and L. acidophilus. In the mostpreferred embodiment of the invention, L. delbrueckii is the predominantdesired bacteria. It is known that L. delbrueckii exists in severalsubspecies and the present invention includes the use of all subspecies,mutations, and genetic alterations to L. delbrueckii.

Inoculation with euhygienic bacteria is preferably performed subsequentto other bacterial control measures being taken, for example, afterdehairing the animal, applying an acetic acid spray wash, applyingantimicrobial agents or after irradiating the food. Under properenvironmental conditions, euhygienic bacteria proliferate and colonizethe food surface, and in so doing, create a pH environment favorable tothe continued competitive growth of the euhygienic bacteria.

While not intending to be bound by theory, it is believed that one ofthe ways in which certain euhygienic bacteria act to extend the shelflife of meat is by lowering the pH on the surface of the meat to createa slightly acidic environment. The lowering of the pH on the surface ofthe meat creates an environment favorable to the growth of theeuhygienic bacteria, but unfavorable to the growth of undesiredbacteria. Thus, once a colony of euhygienic bacteria, such as L.delbrueckii, is established on the surface of a meat product, otherforms of bacteria are effectively precluded from multiplying or arekilled by the acidic environment produced by the euhygienic bacteria.

In another embodiment of the invention, the inoculation of meat witheuhygienic bacteria is done in combination with the inoculation of afood product either with antibiotics or with antibiotic producingbacteria, for example, Streptococcus Lactose or Pediococcus. Suchbacteria are known to generate antibiotics toxic to spoilage andpathogenic bacteria. These later bacteria are capable of producingantibiotics toxic to undesired pathogenic and spoilage bacteria, butthat are not toxic to euhygienic bacteria. It is also within the scopeof the present invention that a euhygienic bacteria may be geneticallyengineered to acquire certain antibiotic properties. Thus, inoculationwith such an euhygienic bacteria may actively kill certain undesiredbacteria while proliferating on the surface of a food product toeffectively inhibit and/or exclude the growth of other undesiredbacteria.

In another embodiment of the invention, the euhygienic bacteria used isa gram negative, sacrophilic, mesophilic, thermophilic bacteria,effective to competitively inhibit the growth of spoilage and pathogenicbacteria. In a particular embodiment of the present invention, aneuhygienic bacteria of the genus Hafnia and more preferably from thespecies alvei is used either independently or in conjunction with L.delbrueckii.

Although not intending to be restricted by current theory, it isbelieved that L. delbrueckii bacteria may be present on meat surfaces ina symbiotic relationship with other commensal euhygienic bacteria. Forexample, L. delbrueckii may proliferate on meat surfaces with HafniaAlvei in such a relationship. Although Hafnia Alvei is known to be acommon bacteria, a sub-species of Hafnia Alvei is known to be capable ofrelatively rapid growth at temperatures of about 5° C. Under one theory,Hafnia Alvei initially colonizes the surface of a food product to createan environment conducive to the growth of L. delbrueckii. Therefore, thepresent invention includes the inoculation of meat with either HafniaAlvei or L. delbrueckii, or a combination thereof, in order tocompetitively inhibit and exclude the growth of undesired pathogenic andspoilage bacteria.

In a preferred embodiment, euhygienic bacteria such as L. delbrueckiibacteria is contacted with an animal carcass after the animal has beenthrough one or more bacterial control measures to reduce the number ofbacteria on the meat surface. For example, after an animal has beendehaired and its carcass has been conveyed through an acetic acid spraywash, the carcass is inoculated with an effective amount of theeuhygienic bacteria, L. debrueckii. In such a manner, the inoculationwith L. delbrueckii is more effective in inhibiting the growth ofundesired bacteria due to the reduction of other bacteria on the meatsurface.

Certain acidophilic euhygienic bacteria, such as lactobaccillium, areknown to grow well in acidic environments having pH ranges from 3 to 7.Fresh meat is known to have a pH of about 5.3 to about 7. At pH levelsof about 4.5 the majority of spoilage and pathogenic bacteria are eitherkilled or their growth is severely inhibited and/or arrested. Contactingfresh meat with an effective amount of a weak organic acid, such asacetic or lactic acid, lowers the pH of the meat from about pH 3 andabout pH 5 and preferably to about 4, thereby reducing the vast majorityof non-acidophilic bacteria and creating an environment more conduciveto the promoting the growth of acidophilic euhygienic bacteria. Theacidification of the surface of red meat also has other beneficialeffects. Organic acids act to maintain meat in a reduced state, therebymaintaining a desirable red color of the meat. The present inventiontherefore includes a method for creating an acidic environment on thesurface of a meat product favorable to the growth of acidophiliceuhygienic bacteria.

It is to be understood that inoculation of ground food products mayentail contacting euhygienic bacteria with portions of the food productwhich will not be necessarily "on the surface" of the food product. Itis believed that euhygienic bacteria, even when present on the interiorof a food product, such as ground beef, promotes the competitiveinhibition and/or exclusion of the growth of undesired bacteria. It isfurther believed that the use of euhygienic bacteria is particularlyuseful in ground meat products incorporating vegetative matter, such asoat flour.

The present invention also includes an unique method for tenderizingmeat whereby meat is allowed to age for an extended period of timewithout spoiling. The aging of meat permits enzymes present in meat todegrade meat fiber, thus making the meat more tender. The freezing ofmeat retards or ceases such enzymatic activity. Irradiation of meatsimilarly destroys or retards enzymatic reactions that would otherwiseoccur. The present invention, because it allows for the maintenance ofmeat in a refrigerated environment for an extended period of timewithout spoiling, permits the natural enzymatic aging of the meat toproceed, producing meat of increased tenderness. In one embodiment ofthe present invention, meat is inoculated with an effective amount ofeuhygienic bacteria to inhibit and/or exclude the growth of undesiredbacteria for a period of time sufficient to permit the natural enzymaticaging of meat without any coincidental spoilage of the meat.

Another aspect of the present invention includes exposing euhygienicbacteria to a meat processing facility, or the equipment used in such afacility subsequent to the effective sterilization of such facilityand/or equipment. In such a manner, the general environment of the meatprocessing facility is effectively exposed to or inoculated witheuhygienic bacteria in order to competitively inhibit and/or exclude thegrowth of undesired pathogenic and spoilage bacteria. In this way, forexample, the risk of unintended contact between meat products andundesired bacteria is kept to a minimum and the opportunity forundesired bacterial infection of meat is vastly reduced. The exposure orinoculation of a food processing facility with euhygienic bacteria canbe accomplished in any manner which effectively reduces the risk ofunintentional infection of a food product with undesired bacteria. Thiscan be accomplished, for example, by first effectively sterilizing afood processing facility, or the equipment therein, by applying to thefacility and equipment effective amounts and concentrations of organicacid solutions and/or other sanitizers, such as, but not limited to,chlorine, quaternary ammonia, and iodine based agents. After suchsterilization, the facility and equipment therein is inoculated with aneffective amount of euhygienic bacteria to inhibit and/or exclude thegrowth of undesired bacteria.

It is to be expressly understood that the present invention can be usedin combination with other bacterial control procedures. In particular,the dehairing of animals, or the spraying of animal carcasses withorganic acid solutions, prior to the dispatching and slaughtering ofsuch animals can be used to initially reduce the number of bacteriapresent in the meat slaughtering facility. Moreover, sanitation measuresincluding the sterilization of knives used in the slaughtering process,changing of worker's gloves on a periodic basis during the slaughteringoperation, disinfecting of slaughtering lines and maintaining personalhygiene requirements for workers, assists in the control of undesiredbacteria proliferation. By using the present invention in combinationwith such other sanitation measures, and by maintaining meat in anenvironment cooled to about -1° C.-7° C. after the vacuum packing of themeat in plastic bags, it has been found that the shelf life of meat canbe extended for up to 150 days without unacceptable growth of spoilageand pathogenic bacteria. The general object of the present invention isthus to create an environment that selectively favors the growth andproliferation of euhygienic hygiene bacteria over the growth ofundesired bacteria.

In one embodiment of the invention, a second inoculation with euhygienicbacteria is performed prior to the final packaging of meat products inoxygen impermeable wrapping such as a plastic bag. In this embodiment,meat is placed in plastic bags, contacted with euhygienic bacteria, andambient air is then vacuumed from the bag and the bag is sealed. In sucha manner, euhygienic bacteria colonize the meat within the substantiallyanaerobic environment of the vacuum packed bag. Food products, such asmeat, treated and packaged as described above, can be placed in arefrigerated environment to further extend the shelf life of the foodproduct.

In another embodiment of the invention, a food product first inoculatedwith euhygienic bacteria is maintained in a temperature environmentcooled to between about -1° C. to about 7° C., more preferably betweenabout 1° C. and 6° C., and most preferably between about 2° C. and 5° C.It is preferable to maintain meat at a temperature above the approximatefreezing point of meat (about -2.5° C. to about -3° C.) in order toavoid the damage caused by freezing meat and to avoid the killing orsevere retardation and/or arrestation of euhygienic bacterial growth andproliferation. It will be appreciated that variations in temperature andperiods of exposure may be utilized. However, lower temperatures andlonger periods of exposure produce a greater depth of temperaturepenetration of the meat product and detract from the product quality.The present invention also includes the inoculation of food productswith euhygienic bacteria genetically altered to grow and proliferate inlow temperature environments.

In some situations, the packaging of a food product may be necessary forthe present invention to be used effectively, i.e., in order thateuhygienic bacteria may effectively colonize the food product. Forexample, dependent upon several factors, including but not limited tothe kind of undesired bacteria in the ambient environment, the type offood product, and other environmental conditions, a food product mayrequire packaging in an oxygen impermeable plastic bag subsequent toinoculation with an effective amount of euhygienic bacteria. In generalterms, environmental conditions must be created and maintained so thatthe natural selection and growth of euhygienic bacteria is favored overthat of undesired bacteria.

The present invention also comprises food products made in accordancewith the various embodiments of the above-described method. Inparticular, the present invention includes a meat product having a shelflife of over about 40 days produced in accordance with the methodcomprising the inoculation of meat with an effective amount ofeuhygienic bacteria to competitively inhibit the growth of pathogenic orspoilage bacteria. The euhygienic bacteria are preferably selectedeither from the genus Lactobacillus and more preferably from the speciesL. delbrueckii, or from the genus Hafnia, and more preferably from thespecies alvei. In one embodiment, the meat is maintained in storage at atemperature environment of between about -1° C. and 7° C., morepreferably between about 2° C. and 7° C., and most preferably betweenabout 3° C. and 5° C.

Meat produced in accordance with the above-described method retains thecolor and odor characteristics associated with fresh meat for anextended period of time, such time period extending up to about 150 daysfrom the date the animal was slaughtered. Because conventional methodsof fresh meat processing do not allow for meat shelf life of over about30 to 40 days, numerous foreign markets for fresh domestic meat productsremain effectively closed. Access to foreign fresh meat markets, forexample, those of the Pacific Rim countries and Europe, necessitate thecostly shipping of domestic meat products by air in order to have suchproducts sold before spoilage occurs. The present invention extends theshelf life of fresh meat and meat by-products for up to about 150 daysor more without the undesired proliferation of spoilage or pathogenicbacteria. Because of this extended shelf life, foreign markets fordomestic fresh meat products are made accessible, allowing for theeconomic shipment of fresh meat by boat, rather than by airplane.

The following test results are provided for purposes of illustration andare not intended to limit the scope of the invention.

EXAMPLES Example 1

An animal was slaughtered in a process in which the animal was firststunned, de-haired, ex-sanguinated, dehided, conveyed through an aceticacid spray wash (acetic acid present in a 0.5-1.5% solution) andfabricated. After application of the acetic acid spray, the animalcarcass was sprayed with a diluted solution containing L. delbrueckiibacteria formulated by growing L. delbrueckii in 750 ml of growth brothfor 24 hours at a temperature of 35° C. and diluting the resultingsolution to attain a 1 part in 10 solution. Meat from the animal carcasswas then vacuum packed in a plastic bag to remove essentially all oxygenand the bag was heat sealed. The meat was stored in a temperatureenvironment of about 5° C. for 150 days. After 150 days, the bag wasopened and a total bacterial plate count was performed. An analysis ofthe bacteria present on the meat was performed indicating that L.delbrueckii bacteria had essentially colonized the entire meat surface.The meat had color characteristics similar to meat that had beenslaughtered in a conventional fashion and refrigerated at 5° C. for lessthan 30 days.

Example 2

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe scope of the present invention as set forth in the following claims.

What is claimed is:
 1. A method for preserving a food product,comprising the steps of:reducing the number of bacteria on a foodproduct, wherein said step of reducing comprises dehairing an animal tobe slaughtered prior to dispatching said animal and applying an organicacid to said animal; inoculating the surface of the food product with aneffective amount of non-spoilage and non-pathogenic bacteria effectiveto competitively inhibit the growth of pathogenic and spoilage bacteria;maintaining said food product in a temperature environment thatselectively favors the proliferation of said non-spoilage andnon-pathogenic bacteria; and packaging the food product in asubstantially oxygen impermeable package.
 2. A method for preserving ameat product, comprising:dispatching an animal; de-hiding an animal;contacting said animal with an organic acid solution; inoculating meatfrom said animal with an effective amount of non-spoilage andnon-pathogenic bacteria to competitively inhibit the growth of spoilageand pathogenic bacteria, said step of inoculating said meat performedsubsequent to said step of contacting said meat with said organic acidsolution; fabricating said animal; vacuum packaging said fabricatedanimal meat in a plastic bag.
 3. A method for preserving a food product,comprising:(a) reducing the total number of bacteria on a food productto below about 5,000 microorganisms per gram of food product; and (b)inoculating the food product with an amount of non-spoilage andnon-pathogenic bacteria to inhibit the growth of spoilage and pathogenicbacteria, wherein said non-spoilage and non-pathogenic bacteria do notproduce commercially unacceptable amounts of metabolic byproductsselected from the group consisting of carbon dioxide, methane,nitrogenous compounds, butyric acid, propionic acid, lactic acid, formicacid, sulfur compounds, and mixtures thereof.
 4. A method for preservinga food product comprising:(a) cleaning said food product to removespoilage and pathogenic bacteria present on said food product from saidfood product; (b) colonizing said food product with non-spoilage andnon-pathogenic bacteria to an extent effective to competitively inhibitthe growth of spoilage and pathogenic bacteria on said food product; and(c) packaging the food product in a substantially oxygen impermeablepackage to prevent infection of said cleaned and colonized food productwith spoilage and pathogenic bacteria.
 5. The method of claim 4, whereinsaid non-spoilage and non-pathogenic bacteria are homofermentive, grampositive Lactobacillus bacteria able to proliferate at temperatures fromabout -1° C. to about 35° C.